1. Field of the Invention
This invention relates generally to slide bearings, and particularly to slide bearing pads suitable for placement between various superstructures and their supporting bases so as to permit the superstructures to move in accordance with various forces such as thermal expansion and contraction, winds, and changes in the amount of weight being supported by the superstructures.
2. Description of the Prior Art
Various structures which employ open frameworks for carrying the load of the structure are conventionally provided with a bearing pad intended to permit sliding movement between an associated structural member of the structure and a foundation or other base supporting the structural member.
U.S. Pat. No. 3,243,236, issued Mar. 29, 1966 to J. M. Graham, discloses a low-friction bearing pad intended for use with structures as described above wherein a piece of sheet bearing material, such as polytetrafluoroethylene is bonded to a pad of elastomeric material as by an epoxy adhesive, and the like. Further, U.S. Pat. No. 3,397,856, issued Aug. 20, 1968 to D. J. Sullivan et al, discloses a structural bearing pad wherein a layer of polytetrafluoroethylene is bonded to a perforated metal plate itself embedded in a pad constructed from an elastomeric material such as neoprene. The latter mentioned reference stipulates that the film or sheet of the bearing material must first be etched in a known manner before a layer of a suitable adhesive, such as a heat-activatable epoxy resin, is applied to the bearing material in order to adhere same to the perforated metal plate. The reason for this etching of the sheet of bearing material prior to adherence thereof to the backing plate or pad is that nonpolar polymeric substrates such as polytetrafluoroethylene are very difficult to adhesively bond, and they must be chemically treated to introduce polar sites on the surface of the material. Not only is this necessary chemical treatment expensive and time consuming, but the resulting bond is still the weakest link in the resulting slide bearing and limits the maximum loads and temperatures which such bearings can withstand.
Various proposals have been made for facilitating attachment of adhering polymeric bearing materials, such as tetrafluoroethylene, to metal backing members. Examples of the use of perforated backing members to facilitate adherence can be found in U.S. Pat. Nos. 2,622,949, issued Dec. 23, 1952 to Louis M. Cotchett; 2,976,093, issued Mar. 21, 1961 to V. G. Reiling. In addition, U.S. Pat. No. 2,051,373, issued Aug. 18, 1936 to P. J. Fitzgerald, discloses the use of upstanding tabs on sheet metal or the like in order to facilitate binding to the sheet metal fibers or yielding materials such as used to construct brake linings, gaskets, and the like.